Synchromesh. Eventually you will not be able to access some gears at all. If you are planning on racing the car and making some serious power, then its time to rebuild. If you just do some light spirited runs, drive the car lightly and not planning to mod, then just swap in used trans, thats what I did.

If this applies to all gears it more likely to be the clutch not the gearbox sounds to me like somthing keeping the first motion shatf spinning so to sycros can't slow the gears enought check the hydrulics first clutch slave cylinders are common on E30s check the level of fluid if its down find the leak . If all thats OK remove the gearbox and check the clutch not just for waer but make sure everything slides freely ie friction plate on shaft and release bearing on its tube. If you need any info on removing the box or changing the hydraulics let me know.